Charging apparatus and charging method

ABSTRACT

In the case of charging by a charging apparatus having a plurality of input terminals to which external power sources for charging a secondary battery are inputted, it is prevented that a current of the inputted power source is outputted to the outside from the other input terminals for charging which are not used. If there are inputs from a plurality of input terminals, the input power sources are controlled so that the battery is optimally charged. pnp-type transistors Q 1  and Q 2  are arranged between two input terminals of a terminal  11  for an external power adaptor and a terminal  12  for a holder and a secondary battery E 1 , respectively. When a control IC  13  detects an input power voltage of one of the transistors, the transistor on the detected side is turned on. If the control IC  13  detects both input power voltages, a priority is allocated under predetermined conditions and the secondary battery E 1  is charged by the power source of the higher priority.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.10/426,661 filed on May 1, 2003 which is hereby incorporated in itsentirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a charging apparatus and a charging method.More particularly, the invention is suitable when it is applied to acharging apparatus and a charging method of a secondary battery of acellular phone or the like having two or more input terminals forcharging.

2. Description of the Related Arts

A primary battery such as a dry battery, and a secondary battery, suchas nickel-cadmium battery, nickel-hydrogen battery, or lithium-ionbattery, or the like, are used as a power source of a portableelectronic apparatus. Even if the secondary battery is dead, the batterycan be repetitively used by being charged. However, it is very tiringthat each time the battery is dead, the user removes the secondarybattery from the portable electronic apparatus and charges it by acharger. Therefore, a cellular phone or the like has a structure suchthat it can be charged in a state where the secondary battery is held inthe main body.

As a method of charging the cellular phone in a state where thesecondary battery is held in the main body, for example, there is amethod whereby a home-use, commercially available, AC power source isused as an external power source, and the charge is performed by usingan AC adaptor or a method whereby a battery of an automobile is used asan external power source and the charge is performed via a cigarettesocket, a vehicle-mounted adaptor, or the like. Among recent portableelectronic apparatuses, there is an apparatus having a socket into whicha terminal of the adaptor for each of those external power sources isdirectly inserted and the charge is performed. Further, there is anapparatus, such as cellular phone, MD (mini disc) player, or the like,such that merely by putting it onto a holder connected to the adaptorfor the external power source, the charge can be performed.

The ordinary cellular phone has two charging terminals, such as acharging terminal for the holder and a charging terminal for theadaptor, so that in a use location, such as a home or the like,importance is attached to the easiness of the charging operation and thecharge can be performed via the holder connected to the adaptor for theexternal power source, and in a mobile location, such as outdoor, roomin an automobile, or the like, importance is attached to the easiness ofcarrying and the charge can be performed only by the adaptor for theexternal power source. In order to make the apparatus cope with such aplurality of charging methods, by providing a plurality of charginginput terminals for the portable electronic apparatus, the user caneasily charge it.

A charging apparatus of such a conventional, portable electronicapparatus having a plurality of charging terminals will now bedescribed. FIG. 1 is a diagram showing an example of a conventionalcharging circuit of a cellular phone. The charging circuit isconstructed of: a terminal 101 for an external power adaptor; a terminal102 for a holder; diodes D101 and D102; a pnp-type transistor Q101;resistors R101 and R102; a control IC 103; and a secondary battery E101.

The terminal 101 for the external power adaptor is an input terminal fordirectly connecting a connecting terminal of the adaptor for theexternal power source and inputting a DC power source converted by theexternal power adaptor. The terminal 101 for the external power adaptorcomprises a terminal 101 a of a plus (+) electrode and a terminal 101 bof a minus (−) electrode. The terminal 102 for the holder is an inputterminal for connecting to a terminal of the holder to which the adaptorfor the external power source has been connected and inputting a DCpower source converted by the adaptor for the external power source viathe holder. The terminal 102 for the holder comprises a terminal 102 aof a plus electrode and a terminal 102 b of a minus electrode. Thesecondary battery E101 is a battery, such as lithium-ion battery,nickel-hydrogen battery, or the like, of what is called a cellularphone.

The terminal 101 a is connected via the diode D101 and the terminal 102a is connected via the diode D102 to an input electrode, that is, anemitter of the pnp-type transistor Q101, and the control IC 103,respectively. An output electrode, that is, a collector of the pnp-typetransistor Q101, is connected to a plus side of the secondary batteryE101 via the resistor R101. Both ends of the resistor R101 are connectedto the control IC 103. Further, a control electrode, that is, a base ofthe pnp-type transistor Q101, is connected to the control IC 103 via theresistor R102. A minus side of the secondary battery E101 and a part ofthe control IC 103 are connected to the terminals 101 b and 102 b.

In the charging circuit, if a current of an external power voltage isinputted from the terminal 101 a, the diode D101 is turned on by aforward bias, so that the current of the power voltage is supplied tothe pnp-type transistor Q101 and the control IC 103. When the control IC103 detects the voltage as mentioned above, the current is supplied tothe base of the pnp-type transistor Q101 via the resistor R101 undercontrol of the control IC 103. Thus, the pnp-type transistor Q101 isturned on, a portion between the emitter and the collector of thepnp-type transistor Q101 is made conductive, and the secondary batteryE101 is charged via the resistor R101.

If the current of the external power voltage is inputted from theterminal 102 a, the diode D102 is turned on by a forward bias, so thatthe current of the power voltage is supplied to the pnp-type transistorQ101 and the control IC 103. When the control IC 103 detects the voltageas mentioned above, the current is supplied to the base of the pnp-typetransistor Q101 via the resistor R101 under the control of the controlIC 103. Thus, the pnp-type transistor Q101 is turned on, the portionbetween the emitter and the collector of the pnp-type transistor Q101 ismade conductive, and the secondary battery E101 is charged via theresistor 101.

In the case of charging by the charging circuit, a constant voltage, aconstant current, or the like to the secondary battery E101 is measuredand the charging circuit is controlled by the control IC 103 so that thecharge is performed by a desired voltage or current. For example, if afull charge is detected, the control IC 103 stops the current supply tothe base of the pnp-type transistor Q101 and stops the charge. Asmentioned above, in the charging circuit shown in FIG. 1, when thecurrent of the external power voltage is inputted from the terminal 101a, the diode D101 is turned on by the forward bias and the current ofthe power voltage is supplied to the pnp-type transistor Q101 and thecontrol IC 103. At this time, since a backward bias is applied in thediode D102, the diode D102 is turned off and the current is hardlysupplied to the terminal 102 a. Similarly, when the current of theexternal power voltage is inputted from the terminal 102 a, the diodeD102 is turned on by the forward bias and the current of the powervoltage is supplied to the pnp-type transistor Q101 and the control IC103. At this time, since a backward bias is applied in the diode D101,the diode D101 is turned off and the current is hardly supplied to theterminal 101 a.

That is, a situation such that when the external power source isinputted from one of the input terminals for charging, it is outputtedfrom the other input terminal for charging is prevented by usingunilaterality of the diode.

However, the foregoing conventional charging apparatus and chargingmethod have the following problems. FIGS. 2A and 2B are diagrams showingan example for explaining a voltage and a current between a diode and atransistor. FIG. 2A is a diagram regarding the voltage, and FIG. 2B is adiagram regarding the current. As shown in FIG. 2A, when a voltage thatis obtained after the output from the diode is assumed to be Vq and avoltage that is inputted to the diode D101 is assumed to be Vd1, it isnecessary to set Vd1 to be higher than Vq in order to obtain apredetermined voltage Vq. Similarly, when a voltage that is inputted tothe diode D102 is assumed to be Vd2, it is necessary to set Vd2 to behigher than Vq in order to obtain the predetermined voltage Vq. This isbecause a voltage drop (drop voltage) is caused by the diode.

Therefore, the diode is used so that the power voltage inputted to thecharging circuit is not outputted from the other input terminal forcharging, and in order to obtain the predetermined voltage, it isnecessary that the input voltage to the diode is set to be higher by thedrop voltage. There is, consequently, a problem such that the efficiencyof the charging circuit deteriorates.

As shown in FIG. 2B, when the power voltage is inputted to both of thediodes D101 and D102, when a current flowing in the diode D101 isassumed to be Id1 and a current flowing in the diode D102 is assumed tobe Id2, a merged current Iq is equal to Iq=Id1+Id2 (a base current ofthe transistor Q101 serving as an operation current is ignored).

Therefore, when the power voltages are simultaneously inputted to thecharging circuit from a plurality of charging terminals, since powersource currents also flow from a plurality of charging terminals, anovercurrent flows to the secondary battery and the charging circuit andan adverse influence is exerted thereto. There is a problem that thereis a possibility of deterioration in safety of the charging apparatus.

OBJECTS AND SUMMARY OF THE INVENTION

In a charging apparatus having a plurality of input terminals that areused for charging, therefore, it is an object of the invention toprovide a charging apparatus and a method in which safety is assured andefficiency is high. To accomplish the above object, according to thefirst aspect of the invention, there is provided a charging apparatuscomprising:

-   -   first and second input terminals to which power voltage sources        are connected;    -   first and second semiconductor devices for power control in        which the first and second input terminals are connected to        input electrodes, respectively;    -   a secondary battery to which output electrodes of the first and        second semiconductor devices for power control are connected in        common and that is connected between the common connection        electric potential point and a reference electric potential        point;    -   a control circuit for controlling a terminal voltage and a        charge current of the secondary battery to desired values; and    -   switching signal generating means for detecting voltages that        are generated at the input electrodes of the first and second        semiconductor devices for power control and generating a        switching signal for turning on a circuit between the input and        output electrodes of the semiconductor device for power control        at which the voltage has been detected.

According to the invention, the semiconductor devices for power controlare respectively provided between the first and second input terminalsand the secondary battery, the voltage generated at each input electrodeof the semiconductor devices for power control is detected, and theon/off states of the circuit between the input and output electrodes ofthe semiconductor device for power control are switched in accordancewith a detection result, so that while the flow of current from theinput terminal to which no power source is inputted is prevented, theswitching of power sources with high safety and high efficiency can berealized.

The above and other objects and features of the present invention willbecome apparent from the following detailed description and the appendedclaims with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of a charging circuit of aconventional cellular phone;

FIGS. 2A and 2B are diagrams showing an example for explaining a voltageand a current between a diode and a transistor in the charging circuitof the conventional cellular phone;

FIGS. 3A to 3C are schematic diagrams showing an example of a cellularphone having two input terminals of an external power source forcharging;

FIGS. 4A and 4B are schematic diagrams of an example showing a chargingstate of the cellular phone;

FIG. 5 is a block diagram showing an example of a charging circuitaccording to the first embodiment of the invention;

FIG. 6 is a block diagram showing an example of a charging circuitaccording to the second embodiment of the invention;

FIG. 7 is a block diagram showing an example of a charging circuitaccording to the third embodiment of the invention;

FIG. 8 is a block diagram showing an example of a charging circuitaccording to the fourth embodiment of the invention;

FIG. 9 is a block diagram showing an example of a charging circuitaccording to the fifth embodiment of the invention;

FIG. 10 is a block diagram showing an example of a charging circuitaccording to the sixth embodiment of the invention; and

FIG. 11 is a block diagram showing an example of a charging circuitaccording to the seventh embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, a portable electronic apparatus to which the invention is appliedwill be described with reference to the drawings. FIGS. 3A to 3C show anexample of a cellular phone having two input terminals of external powersources for charging. A cellular phone 1 shown in FIG. 3A is what iscalled a folding cellular phone and has: a connector 2 to which aconnecting terminal of an external power adaptor, such as an AC adaptor,or the like is directly connected and through which a battery in thecellular phone can be charged; and a terminal portion 3 through whichthe battery in the cellular phone can be charged from the external poweradaptor via a holder 5 (refer to FIG. 4B). FIG. 3B shows an enlargeddiagram of the connector 2. FIG. 3C shows an enlarged diagram of theterminal portion 3.

The connector 2 shown in FIG. 3B is a connector for an externalinterface of the cellular phone 1 and has a terminal 11 a of a plus (+)electrode and a terminal 11 b of a minus (−) electrode serving as powerterminals. In the embodiment, the terminals 11 a and 11 b are referredto as a terminal 11 for the external power adaptor. By connecting theconnecting terminal of the external power adaptor, for example, the ACadaptor, to the connector 2, a secondary battery provided for thecellular phone 1 can be charged.

The terminal portion 3 shown in FIG. 3C has a terminal 12 a of a plus(+) electrode and a terminal 12 b of a minus (−) electrode through whichthe secondary battery can be charged from the external power source viathe holder. It is assumed that the terminals 12 a and 12 b are referredto as a terminal 12 for the holder. By putting the cellular phone 1 ontothe holder so that the terminal 12 for the holder comes into contactwith a terminal provided for the holder, the secondary battery providedfor the cellular phone 1 can be charged.

FIGS. 4A and 4B are diagrams of an example showing a charging state ofthe cellular phone. FIG. 4A is a diagram showing a state where an ACadaptor 4 is connected to the cellular phone and the battery is beingcharged. FIG. 4B is a diagram showing a state where the battery is beingcharged by using the holder 5.

That is, in the charge shown in FIG. 4A, by connecting the AC adaptor 4to the connector 2 of the cellular phone 1 and inserting an electricplug of the AC adaptor 4 into an outlet 6, a predetermined DC powersource is inputted from the terminal 11 for the external power adaptorinto a charging circuit in the cellular phone 1. In the charge shown inFIG. 4B, by putting the cellular phone 1 onto the holder 5 so that theterminal 12 for the holder 1 comes into contact with the terminalprovided for the holder 5 and inserting the electric plug of the ACadaptor 4 connected to the holder 5 into the outlet 6, a predeterminedDC power source is inputted into the charging circuit in the cellularphone 1 via the terminal 12 for the holder. Although the explanation hasbeen made here on the assumption that a home-use, commercially availablepower source is used as an external power source, a battery of anautomobile or the like also can be used.

The charging apparatus according to the invention can be applied to theelectronic apparatus having a plurality of external power inputterminals for charging as described above. The embodiment of theinvention will be described hereinbelow. First, the charging apparatusaccording to the first embodiment of the invention will be described.

FIG. 5 is a diagram showing an example of a charging circuit accordingto the first embodiment of the invention. The charging circuit accordingto the first embodiment is constructed of: the terminal 11 for theexternal power adaptor; the terminal 12 for the holder; pnp-typetransistors Q1 and Q2; resistors R1, R2, and R3; a control IC 13; and asecondary battery E1.

As described above with reference to FIGS. 3A-3C, the terminal 11 forthe external power adaptor is an input terminal to which the connectingterminal of the external power adaptor such as an AC adaptor 4 or thelike is directly connected and through which a predetermined DC powersource converted by the adaptor for the external power source isinputted. The terminal 11 is constructed by the terminal 11 a of theplus electrode and the terminal 11 b of the minus electrode. Theterminal 12 for the holder is an input terminal that comes into contactwith the terminal provided for the holder 5 to which the external poweradaptor has been connected and through which the predetermined DC powersource converted by the adaptor for the external power source isinputted via the holder. The terminal 12 is constructed by the terminal12 a of the plus electrode and the terminal 12 b of the minus electrode.

The secondary battery E1 is a secondary battery, such as lithium-ionbattery, nickel-hydrogen battery, or the like, which is used as abattery of what is called a cellular phone. In the charging circuit, thepnp-type transistors Q1 and Q2 performs a switching operation of theexternal power source that is inputted and control the voltage and thecurrent. The control IC 13 detects a charging voltage, a chargingcurrent, or the like, controls the pnp-type transistors Q1 and Q2, andmakes other controls of the charging circuit.

In the charging circuit, the terminal 11 a is connected to an inputelectrode, that is, an emitter of the pnp-type transistor Q1, and thecontrol IC 13. The terminal 12 a is connected to an input electrode,that is, an emitter of the pnp-type transistor Q2, and the control IC13. Output electrodes, that is, collectors of the pnp-type transistorsQ1 and Q2, are connected to a plus side of the secondary battery E1 viathe resistor R1. Both ends of the resistor R1 are connected to thecontrol IC 13. A control electrode, that is, a base of the pnp-typetransistor Q1, is connected to the control IC 13 via the resistor R2. Acontrol electrode, that is, a base of the pnp-type transistor Q2, isconnected to the control IC 13 via the resistor R3. A minus side of thesecondary battery and a part of the control IC 13 are connected to theterminals 11 b and 12 b, respectively.

Subsequently, in the charging circuit according to the first embodimentconstructed as mentioned above, the operation in the case where thebattery is charged from the input terminal of one of the terminal 11 forthe external power adaptor and the terminal 12 for the holder uponcharging will be described.

In the charging circuit according to the first embodiment, in the caseof charging by using the terminal 11 for the external power adaptor, thecurrent of the external power voltage is inputted from the terminal 11a. The inputted current of the external power voltage is inputted to theemitter of the pnp-type transistor Q1 and the control IC 13. Thus, thecontrol IC 13 detects the power voltage at the emitter of the pnp-typetransistor Q1, that is, in the input electrode portion. When the powervoltage is detected, the control IC 13 supplies the current to the baseof the pnp-type transistor Q1 via the resistor R2. Thus, the pnp-typetransistor Q1 is turned on, a circuit between the emitter and thecollector of the pnp-type transistor Q1 is made conductive, and thesecondary battery E1 is charged via the resistor R1.

In the case of charging by using the terminal 12 for the holder, thecurrent of the external power voltage is inputted from the terminal 12a. The inputted current of the external power voltage is inputted to theemitter of the pnp-type transistor Q2 and the control IC 13. Thus, thecontrol IC 13 detects the power voltage at the emitter of the pnp-typetransistor Q2, that is, in the input electrode portion. When the powervoltage is detected, the control IC 13 supplies the current to the baseof the pnp-type transistor Q2 via the resistor R3. Thus, the pnp-typetransistor Q2 is turned on, a circuit between the emitter and thecollector of the pnp-type transistor Q2 is made conductive, and thesecondary battery E1 is charged via the resistor R1.

In the case of charging by the charging circuit according to the firstembodiment, a constant voltage, a constant current, and the like to thesecondary battery E1 are measured and the apparatus is controlled by thecontrol IC 13 so that the battery is charged by desired voltage andcurrent. If a full charge is detected, the control IC 13 stops thecurrent supply to the bases of the pnp-type transistors Q1 and Q2 andcompletes the charge. In the case of charging, the power voltage that isinputted from the terminal 11 for the external power adaptor or theterminal 12 for the holder is set to be higher than the voltage of thesecondary battery to be charged.

In the charging circuit according to the first embodiment, when thebattery is charged from the input terminal of one of the terminal 11 forthe external power adaptor and the terminal 12 for the holder, thetransistor connected to the input terminal to which the external powersource is inputted is turned on and the transistor connected to theother input terminal is turned off. However, there is also a case whereboth of the terminal 11 for the external power adaptor and the terminal12 for the holder are connected. In such a case, the control IC 13controls the input power sources on the basis of predeterminedconditions. The case of inputting the power sources from both of theinput terminals for charging will be described in conjunction with thesubsequent second to seventh embodiments.

As described above, in the charging circuit according to the firstembodiment, in the case of charging by using the terminal 11 for theexternal power adaptor, the pnp-type transistor Q1 is turned on, thecircuit between the emitter and the collector of the pnp-type transistorQ1 is made conductive, and the current of the power voltage is inputtedto the resistor R1 and the collector of the pnp-type transistor Q2. Atthis time, since no base current flows in the pnp-type transistor Q2,the pnp-type transistor Q2 is turned off. Since the voltage that isinputted to the pnp-type transistor Q2 is also the backward voltage, itis possible to prevent the current from flowing to the terminal 12 a.

Similarly, in the case of charging by using the terminal 12 for theholder, the pnp-type transistor Q2 is turned on, the circuit between theemitter and the collector of the pnp-type transistor Q2 is madeconductive, and the current of the power voltage is inputted to theresistor R1 and the collector of the pnp-type transistor Q1. At thistime, since no base current flows in the pnp-type transistor Q1, thepnp-type transistor Q1 is turned off. Since the voltage that is inputtedto the pnp-type transistor Q1 is also the backward voltage, it ispossible to prevent the current from flowing to the terminal 11 a.

Since the transistor is used as a semiconductor device for preventingthe current from the input terminal for charging from being outputtedfrom the other input terminal for charging, the voltage drop is smallerthan that in the case of using a diode. Therefore, loss of voltage inthe charging circuit can be reduced and charging efficiency is improved.

In the case of charging by using the terminal 11 for the external poweradaptor and the terminal 12 for the holder, control such that the chargeis selectively executed from only one of the external power sources onthe basis of predetermined conditions can be made by the control IC 13or the like. Therefore, heat generation or the like due to theovercurrent upon charging can be prevented and the safety of thecharging circuit and the electronic apparatus having the chargingcircuit can be improved.

Subsequently, a charging apparatus according to the second embodiment ofthe invention will be described. The second embodiment relates to acharging circuit for selecting the input power source by a switchingsignal. In the second embodiment, it is assumed that the external powersource is inputted from one of the two input terminals for charging. Thecase where the power sources are inputted from both of the inputterminals will be explained in the third and subsequent embodiments.

FIG. 6 is a diagram showing an example of the charging circuit accordingto the second embodiment of the invention. The fundamental constructionof the charging circuit is the same as that shown in FIG. 5 anddescribed in the first embodiment. That is, the terminal 11 a isconnected to the emitter of the pnp-type transistor Q1. The terminal 12a is connected to the emitter of the pnp-type transistor Q2. Thecollectors of the pnp-type transistors Q1 and Q2 are connected to theplus side of the secondary battery E1 via the resistor R1. The minusside of the secondary battery is connected to the terminals 11 b and 12b, respectively. Also, in the third to seventh embodiments, which willbe explained below, since their fundamental constructions are similar tothat mentioned above, an explanation of those constructions is omittedin the subsequent embodiments.

Other portions, that is, a control circuit for the pnp-type transistorsQ1 and Q2, are constructed as follows. A Q1 voltage detecting circuit 21is connected to both ends on the emitter side and the collector side ofthe pnp-type transistor Q1 and is a circuit which can detect the voltageof the power source that is inputted from those ends to the pnp-typetransistor Q1. A Q2 voltage detecting circuit 22 is connected to bothends on the emitter side and the collector side of the pnp-typetransistor Q2 and is a circuit which can detect the voltage of the powersource which is inputted from those ends to the pnp-type transistor Q2.

The Q1 voltage detecting circuit 21 and the Q2 voltage detecting circuit22 are connected to a switching signal generating circuit 24. Theswitching signal generating circuit 24 is a circuit for generating aswitching signal on the basis of detection results of the Q1 voltagedetecting circuit 21 and the Q2 voltage detecting circuit 22. Theswitching signal generating circuit 24 is connected to a switchingcircuit 25.

The switching circuit 25 is connected to the bases of the pnp-typetransistors Q1 and Q2 and is a circuit for supplying base currents tothe pnp-type transistors Q1 and Q2 and switching the on/off operationsof the pnp-type transistors Q1 and Q2 on the basis of the switchingsignal that is sent from the switching signal generating circuit 24.

A current detecting circuit 26, a charge stop detecting circuit 27, aconstant current detecting circuit 28, and a constant voltage detectingcircuit 29 construct what is called a charge power stabilizing circuitof the charging circuit. The charge power stabilizing circuit alwaysoperates during the charging operation and monitors the charge power.The current detecting circuit 26 is connected to both ends of theresistor R1 and is a circuit for detecting a current at those ends. Thecurrent detecting circuit 26 is connected to the constant currentdetecting circuit 28 and the charge stop detecting circuit 27.

The constant current detecting circuit 28 is a circuit for detecting theconstant current from the current detected by the current detectingcircuit 26. The charge stop detecting circuit 27 is a circuit fordetecting the charge stop due to a full charge or the like of thesecondary battery E1 from the current detected by the current detectingcircuit 26. The constant voltage detecting circuit 29 is a circuit fordetecting the constant voltage from both ends of the secondary batteryE1. The constant current detecting circuit 28, the charge stop detectingcircuit 27, and the constant voltage detecting circuit 29 are connectedto a control circuit 23.

The control circuit 23 is a circuit for controlling the power sourcethat is inputted so as to be the value that is optimum to charge thesecondary battery on the basis of detection results that are sent fromthe constant current detecting circuit 28, charge stop detecting circuit27, constant voltage detecting circuit 29, and the like and generating acontrol signal in the case where the charge voltage or current is equalto a value other than a specified value or the secondary battery E1 hasbeen fully charged. The control circuit 23 is connected to the switchingcircuit 25 mentioned above. The switching circuit 25 is a circuit foralso switching the on/off operations of the pnp-type transistors Q1 andQ2 corresponding to the control signal when the control signal isreceived from the control circuit 23.

Subsequently, the operation in the case of charging from one of theterminal 11 for the external power adaptor and the terminal 12 for theholder upon charging in the charging circuit according to the secondembodiment will be described.

In the charging circuit, in the case of charging by using the terminal11 for the external power adaptor, the current of the external powervoltage is inputted from the terminal 11 a. The inputted current of theexternal power voltage is supplied to the emitter of the pnp-typetransistor Q1 and the Q1 voltage detecting circuit 21. Therefore, the Q1voltage detecting circuit 21 detects the power voltage of the inputelectrode portion of the pnp-type transistor Q1. A detection result issent to the switching signal generating circuit 24.

The switching signal generating circuit 24 generates the switchingsignal according to the detection result. The generated switching signalis sent to the switching circuit 25. The switching circuit 25 supplies acurrent to the base of the pnp-type transistor Q1 by the switchingsignal from the switching signal generating circuit 24. Thus, thecircuit between the emitter and the collector of the pnp-type transistorQ1 is turned on, that is, made conductive, and the secondary battery E1is charged via the resistor R1.

In the case of charging by using the terminal 12 for the holder, thecurrent of the external power voltage is inputted from the terminal 12a. The inputted current of the external power voltage is supplied to theemitter of the pnp-type transistor Q2 and the Q2 voltage detectingcircuit 22. Therefore, the Q2 voltage detecting circuit 22 detects thepower voltage of the input electrode portion of the pnp-type transistorQ2. A detection result is sent to the switching signal generatingcircuit 24.

The switching signal generating circuit 24 generates the switchingsignal according to the detection result. The generated switching signalis sent to the switching circuit 25. The switching circuit 25 supplies acurrent to the base of the pnp-type transistor Q2 by the switchingsignal from the switching signal generating circuit 24. Thus, thecircuit between the emitter and the collector of the pnp-type transistorQ2 is turned on, that is, made conductive, and the secondary battery E1is charged via the resistor R1.

During the charge of the secondary battery E1, the apparatus iscontrolled so as to operate safely by the charge power stabilizingcircuit and the control circuit 23. That is, the current across theresistor R1 is measured by the current detecting circuit 26 and themeasurement result is sent to the constant current detecting circuit 28.When the constant current detecting circuit 28 detects the constantcurrent from the measurement result, it generates a constant currentdetection signal. The measurement result of the current detectingcircuit 26 also is sent to the charge stop detecting circuit 27. Whenthe charge stop detecting circuit 27 detects the full charge or the likeof the secondary battery from the measurement result, it generates acharge stop signal.

Those constant current detection signal and charge stop signal are sentto the control circuit 23. The constant voltage detecting circuit 29detects a constant voltage from both ends of the secondary battery E1.When the constant voltage is detected, the constant voltage detectingcircuit 29 generates a constant voltage detection signal. The constantvoltage detection signal is sent to the control circuit 23. On the basisof those signals, the control circuit 23 controls the inputted voltageand current of the external power source so as to enter the optimumcharging state.

If the voltage or current of the charging power source is equal to avalue other than the specified value or the charge stop signal is sentfrom the charge stop detecting circuit 27, the control circuit 23 sendsa control signal to the switching circuit 25. The switching circuit 25which received the control signal stops the supply of the base currentsto the pnp-type transistors Q1 and Q2, thereby stopping the charge tothe secondary battery E1.

As described above, in the charging circuit according to the secondembodiment, in the case of charging by using the terminal 11 for theexternal power adaptor, the pnp-type transistor Q1 is turned on, thecircuit between the emitter and the collector of the pnp-type transistorQ1 is made conductive, and the current of the power voltage is inputtedto the resistor R1 and the collector of the pnp-type transistor Q2. Atthis time, since no base current flows in the pnp-type transistor Q2,the pnp-type transistor Q2 is turned off, and since the voltage that isinputted to the pnp-type transistor Q2 is also the backward voltage, itis possible to prevent the current from flowing in the terminal 12 a.

Similarly, in the case of charging by using the terminal 12 for theholder, the pnp-type transistor Q2 is turned on, the circuit between theemitter and the collector of the pnp-type transistor Q2 is madeconductive, and the current of the power voltage is inputted to theresistor R1 and the collector of the pnp-type transistor Q1. At thistime, since no base current flows in the pnp-type transistor Q1, thepnp-type transistor Q1 is turned off, and since the voltage that isinputted to the pnp-type transistor Q1 is also the backward voltage, itis possible to prevent the current from flowing in the terminal 11 a.

Since the transistor is used as a semiconductor device for preventingthe current from the input terminal for charging from being outputtedfrom the other input terminal for charging, the voltage drop is smallerthan that in the case of using the diode. Therefore, loss of voltage inthe charging circuit can be reduced and charging efficiency is improved.Although the operation in the case of charging from one of the charginginput terminals of the terminal 11 for the external power adaptor andthe terminal 12 for the holder upon charging has been described in thesecond embodiment, there is also a case of actually charging from bothof the charging input terminals. In such a case, upon generation of theswitching signal mentioned above, a priority is allocated, as will beexplained in the following embodiments, and only one of the powersources is used in accordance with the priority, so that heat generationor the like due to the overcurrent is prevented and the safety of thecharging apparatus can be held.

The charging apparatus according to the third embodiment of theinvention will be described. It is assumed hereinbelow that in thecharging apparatus according to each of the third to sixth embodiments,the charging power sources are selectively controlled in accordance witha predetermined priority if the power sources are inputted from the twocharging input terminals. Since the case where there the power source isinputted from one of the charging input terminals has already beendescribed in the foregoing second embodiment, its explanation in thesubsequent embodiments is omitted here.

FIG. 7 is a diagram showing an example of a charging circuit accordingto the third embodiment of the invention. In the charging circuitaccording to the third embodiment, control circuits for the pnp-typetransistors Q1 and Q2 are constructed as follows. A Q1 voltage detectingcircuit 31 is connected to both ends on the emitter side and thecollector side of the pnp-type transistor Q1 and is a circuit which candetect the voltage of the power source that is inputted from those endsto the pnp-type transistor Q1. A Q2 voltage detecting circuit 32 isconnected to both ends on the emitter side and the collector side of thepnp-type transistor Q2 and is a circuit which can detect the voltage ofthe power that which is inputted from those ends to the pnp-typetransistor Q2.

The Q1 voltage detecting circuit 31 and the Q2 voltage detecting circuit32 are connected to a priority circuit 34. The priority circuit 34 is acircuit having predetermined priority data such that when the chargingoperation is executed by using both the terminal 11 for the externalpower adaptor and the terminal 12 for the holder, one of them ispreferentially used. The priority circuit 34 is a circuit such that ifthe power voltages are detected from both of the Q1 voltage detectingcircuit 31 and the Q2 voltage detecting circuit 32, a control signalcorresponding to the priority is generated. When the power voltage isdetected only from either the Q1 voltage detecting circuit 31 or the Q2voltage detecting circuit 32, the priority circuit 34 preferentiallyselects the detected one. The priority circuit 34 is connected tocontrol circuits 33 and 35.

The control circuit 33 is connected to the base of the pnp-typetransistor Q1 and is a circuit for supplying the base current to thepnp-type transistor Q1 and switching the on/off operations of thepnp-type transistor Q1 on the basis of the control signal that isreceived from the priority circuit 34. The control circuit 35 isconnected to the base of the pnp-type transistor Q2 and is a circuit forsupplying the base current to the pnp-type transistor Q2 and switchingthe on/off operations of the pnp-type transistor Q2 on the basis of thecontrol signal that is received from the priority circuit 34. In otherwords, the control circuit 33 is the circuit such that if it isdetermined from the control signal from the priority circuit 34 that thepriority of the pnp-type transistor Q1 is higher than that of thepnp-type transistor Q2, the base current is supplied to the pnp-typetransistor Q1, thereby turning on the pnp-type transistor Q1. If it isdetermined that the priority of the pnp-type transistor Q2 is higherthan that of the pnp-type transistor Q1, the base current is supplied tothe pnp-type transistor Q2, thereby turning on the pnp-type transistorQ2.

An overcurrent detecting circuit 36, a charge stop circuit 37, and aconstant voltage detecting circuit 38 construct what is called a chargepower stabilizing circuit of the charging circuit. The overcurrentdetecting circuit 36 is connected to both ends of the resistor R1 and isa circuit for detecting an overcurrent from those ends. The overcurrentdetecting circuit 36 is also connected to the charge stop circuit 37.

The charge stop circuit 37 is a circuit for generating a charge stopsignal when the overcurrent is detected by the overcurrent detectingcircuit 36. The constant voltage detecting circuit 38 is a circuit fordetecting the constant voltage across the secondary battery E1. Thecharge stop circuit 37 and the constant voltage detecting circuit 38 areconnected to the control circuits 33 and 35. In the embodiment, anexplanation regarding the current detecting circuit, charge stopcircuit, constant current detecting circuit, and constant voltagedetecting circuit 38 as a circuit for stabilizing the charge powersource and an explanation regarding the operations of those circuits areomitted.

In the charging circuit according to the third embodiment, the operationin the case where the external power source is inputted from the inputterminals of both the terminal 11 for the external power adaptor and theterminal 12 for the holder upon charging will be explained.

In the charging circuit, in the case of charging by using the terminal11 for the external power adaptor and the terminal 12 for the holder,the currents of the external power voltages are inputted from theterminals 11 a and 12 a. The current of the external power voltageinputted from the terminal 11 a flows in the pnp-type transistor Q1 andthe Q1 voltage detecting circuit 31. Therefore, the Q1 voltage detectingcircuit 31 detects the power voltage of the input electrode portion ofthe pnp-type transistor Q1. The current of the external power voltageinputted from the terminal 12 a flows in the pnp-type transistor Q2 andthe Q2 voltage detecting circuit 32. Therefore, the Q2 voltage detectingcircuit 32 detects the power voltage of the input electrode portion ofthe pnp-type transistor Q2. Detection results of the Q1 voltagedetecting circuit 31 and the Q2 voltage detecting circuit 32 are sent tothe priority circuit 34.

When the priority circuit 34 receives the voltage detection signals fromboth the Q1 voltage detecting circuit 31 and the Q2 voltage detectingcircuit 32, it generates an ON signal on the basis of the presetpriority. The generated ON signal is sent to the control circuit 33 or35. For example, if the apparatus has been set so as to preferentiallyselect the pnp-type transistor Q1, the ON signal is sent to the controlcircuit 33.

When the control circuits 33 and 35 receive the ON signal from thepriority circuit 34, they supply the base currents to the pnp-typetransistors Q1 and Q2, respectively. Thus, the circuit between theemitter and the collector of the transistor having the higher priorityis turned on, that is, made conductive, and the secondary battery E1 ischarged via the resistor R1. When the control circuits 33 and 35 receivethe charge stop signal or the like during the charge, they immediatelystop the supply of the base currents, thereby stopping the charge of thesecondary battery E1.

As described above, in the charging circuit according to the thirdembodiment, in the case of inputting the external power sources fromboth the terminal 11 for the external power adaptor and the terminal 12for the holder and charging, the transistor whose preset priority ishigher between the pnp-type transistors Q1 and Q2 is turned on, thecircuit between the emitter and the collector of such a transistor ismade conductive, and the current of the power voltage is inputted to theresistor R1 and the collector of the other transistor. At this time,since no base current flows in the other transistor, the othertransistor is turned off. Since the voltage that is inputted to theother transistor is also the backward voltage, it is possible to preventthe current from flowing from the other transistor.

Since the transistor is used as a semiconductor device for preventingthe current from the input terminal for charging from being outputtedfrom the other input terminal for charging, the voltage drop is smallerthan that in the case of using a diode. Therefore, loss of voltage inthe charging circuit can be reduced and charging efficiency is improved.

Even if the external power sources are inputted from both the terminal11 for the external power adaptor and the terminal 12 for the holderupon charging, since the apparatus can be controlled so as toselectively use only the preset one of the external power sources, theheat generation or the like due to the overcurrent can be prevented andthe safety of the charging apparatus can be maintained.

Subsequently, a charging apparatus according to the fourth embodiment ofthe invention will be described. In the charging apparatus according tothe fourth embodiment, when the power sources are inputted from the twoinput terminals for charging, the external power source in which thepredetermined voltage value has been detected first is selectively used.

FIG. 8 is a diagram showing an example of a charging circuit accordingto the fourth embodiment of the invention. In the charging circuitaccording to the fourth embodiment, a control circuit for the pnp-typetransistors Q1 and Q2 is constructed as follows. A Q1 voltage detectingcircuit 41 is connected to both ends on the emitter side and thecollector side of the pnp-type transistor Q1 and is a circuit, which candetect the voltage of the external power source that is inputted fromthose ends to the pnp-type transistor Q1. A Q2 voltage detecting circuit42 is connected to both ends on the emitter side and the collector sideof the pnp-type transistor Q2 and is a circuit, which can detect thevoltage of the external power source that is inputted from those ends tothe pnp-type transistor Q2.

The Q1 voltage detecting circuit 41 and the Q2 voltage detecting circuit42 are connected to a preceding signal priority circuit 44. Thepreceding signal priority circuit 44 is a circuit for setting thepriority of the external power source on the side where a predeterminedvoltage has been detected first to be higher and generating a switchingsignal corresponding to the higher priority. In the case of charging acellular phone, for example, the apparatus is set so that the priorityof the external power source on the side where the voltage of 200 mV ormore has been detected first is set to be higher, or the like. If thevoltage is detected only from one of the Q1 voltage detecting circuit 41and the Q2 voltage detecting circuit 42, the power source of the voltagedetecting circuit on the side where the voltage has been detected ispreferentially used. The preceding signal priority circuit 44 areconnected to a switching circuit 45.

The switching circuit 45 is connected to the base of the pnp-typetransistor Q1 and the base of the pnp-type transistor Q2 and is acircuit for supplying a current to the base of the pnp-type transistorQ1 or the base of the pnp-type transistor Q2 and switching the on/offoperations of the pnp-type transistor Q1 or Q2 on the basis of theswitching signal that is received from the preceding signal prioritycircuit 44.

The switching circuit 45 is connected to a control circuit 43. Since thecontrol circuit 43 and the circuits for stabilizing the charge powersource, such as, the overcurrent detecting circuit 46, the charge stopcircuit 47, the constant voltage detecting circuit 48, and the like havealready been described in the second and third embodiments, theirexplanation is omitted here.

In the charging circuit according to the fourth embodiment,subsequently, the operation in the case of inputting the external powersource to the input terminals of both the terminal 11 for the externalpower adaptor and the terminal 12 for the holder upon charging will bedescribed.

In the charging circuit, in the case of charging by using the terminal11 for the external power adaptor and the terminal 12 for the holder,the currents of the external power voltages are inputted from theterminals 11 a and 12 a. The current of the external power voltageinputted from the terminal 11 a flows in the pnp-type transistor Q1 andthe Q1 voltage detecting circuit 41. Therefore, the Q1 voltage detectingcircuit 41 detects the power voltage of the input electrode portion ofthe pnp-type transistor Q1.

The current of the external power voltage inputted from the terminal 12a flows in the pnp-type transistor Q2 and the Q2 voltage detectingcircuit 42. Therefore, the Q2 voltage detecting circuit 42 detects thepower voltage of the input electrode portion of the pnp-type transistorQ2. Detection results of the Q1 voltage detecting circuit 41 and the Q2voltage detecting circuit 42 are sent to the preceding signal prioritycircuit 44.

When the preceding signal priority circuit 44 receives the signals ofthe voltage detection from both of the Q1 voltage detecting circuit 41and the Q2 voltage detecting circuit 42, it preferentially selects theexternal power source on the side where the voltage of the predeterminedvoltage value or more has been detected first and generates theswitching signal on the basis of the priority. The generated switchingsignal is sent to the switching circuit 45.

The switching circuit 45 supplies current to the base of the pnp-typetransistor Q1 or the base of the pnp-type transistor Q2 on the basis ofthe switching signal from the preceding signal priority circuit 44.Thus, the circuit between the emitter and the collector of thetransistor of the higher priority is turned on, that is, madeconductive, and the secondary battery E1 is charged via the resistor R1.

As described above, in the charging circuit according to the fourthembodiment, if the external power sources are inputted from both theterminal 11 for the external power adaptor and the terminal 12 for theholder and charged, the transistor on the side where the predeterminedvoltage value has been detected first between the pnp-type transistorsQ1 and Q2 is turned on, the circuit between the emitter and thecollector of such a transistor is made conductive, and the current ofthe power voltage is inputted to the resistor R1 and the collector ofthe other transistor. At this time, since no base current flows in theother transistor, the other transistor is turned off. Since the voltagethat is inputted is also the backward voltage, it is possible to preventthe current from flowing from the other transistor. Since the transistoris used as a semiconductor device for preventing the current from theinput terminal for charging from being outputted from the other inputterminal for charging, the voltage drop is smaller than that in the caseof using a diode. Therefore, the loss of voltage in the charging circuitcan be reduced and the charging efficiency is improved.

Even if the external power sources are inputted from both the terminal11 for the external power adaptor and the terminal 12 for the holderupon charging, since it is possible to control the apparatus in a mannersuch that only the external power source on the side where the powervoltage has been detected first is selectively used, the heat generationdue to the overcurrent is prevented and the safety of the chargingapparatus can be held.

A charging apparatus according to the fifth embodiment of the inventionwill now be described. In the charging apparatus according to the fifthembodiment, when the power sources are inputted from the two inputterminals for charging, the safer external input power source is higherand is selectively used.

FIG. 9 is a diagram showing an example of a charging circuit accordingto the fifth embodiment of the invention. In the charging circuitaccording to the fifth embodiment, a control circuit for the pnp-typetransistors Q1 and Q2 is constructed as follows. A Q1 voltage detectingcircuit 51 is connected to both ends on the emitter side and thecollector side of the pnp-type transistor Q1 and is a circuit which candetect the voltage of the external power source that is inputted fromthose ends to the pnp-type transistor Q1. A Q2 voltage detecting circuit52 is connected to both ends on the emitter side and the collector sideof the pnp-type transistor Q2 and is a circuit which can detect thevoltage of the external power source that is inputted from those ends tothe pnp-type transistor Q2.

The Q1 voltage detecting circuit 51 and the Q2 voltage detecting circuit52 are connected to a low voltage priority circuit 54. The low voltagepriority circuit 54 is a circuit for setting the priority of theexternal power source on the side where the power voltage is equal to orlarger than a specified minimum input voltage value and the voltage islower to be higher and generating a switching signal corresponding tothe higher priority. For example, when the specified input voltage valueis equal to 280 mV, if the two external power sources of 500 mV and 300mV are inputted, the low voltage priority circuit 54 referentiallyselects the power voltage of 300 mV. If the voltage is detected onlyfrom one of the Q1 voltage detecting circuit 51 and the Q2 voltagedetecting circuit 52, the external power source on the side where thevoltage has been detected is preferentially used. The low voltagepriority circuit 54 is connected to a switching circuit 55.

The switching circuit 55 is connected to the base of the pnp-typetransistor Q1 and the base of the pnp-type transistor Q2 and is acircuit for supplying a current to the base of the pnp-type transistorQ1 or the base of the pnp-type transistor Q2 and switching the on/offoperations of the pnp-type transistor Q1 or Q2 on the basis of theswitching signal from the low voltage priority circuit 54. The switchingcircuit 55 is connected to a control circuit 53. Since the controlcircuit 53 and circuits for stabilizing the charge power source, such ascurrent detecting circuit 56, a charge stop circuit 57, a constantcurrent detecting circuit 58, a constant voltage detecting circuit 59,and the like have already been described in the second and thirdembodiments, their explanation is omitted here.

In the charging circuit according to the fifth embodiment, subsequently,the operation in the case of inputting the external power sources fromthe input terminals of both the terminal 11 for the external poweradaptor and the terminal 12 for the holder upon charging will bedescribed.

In the charging circuit, in the case of charging by using the terminal11 for the external power adaptor and the terminal 12 for the holder,the currents of the external power voltages are inputted from theterminals 11 a and 12 a. The current of the external power voltageinputted from the terminal 11 a flows in the emitter of the pnp-typetransistor Q1 and the Q1 voltage detecting circuit 51. Therefore, the Q1voltage detecting circuit 51 detects the power voltage of the inputelectrode portion of the pnp-type transistor Q1.

The current of the external power voltage inputted from the terminal 12a flows in the emitter of the pnp-type transistor Q2 and the Q2 voltagedetecting circuit 52. Therefore, the Q2 voltage detecting circuit 52detects the power voltage of the input electrode portion of the pnp-typetransistor Q2. The detection results of the Q1 voltage detecting circuit51 and the Q2 voltage detecting circuit 52 are sent to the low voltagepriority circuit 54.

When the low voltage priority circuit 54 receives the signals of thevoltage detection from both the Q1 voltage detecting circuit 51 and theQ2 voltage detecting circuit 52, it preferentially selects the externalpower source on the side where the value of the detected voltage isequal to or larger than the specified minimum input voltage value andthe voltage is lower. The low voltage priority circuit 54 generates aswitching signal on the basis of the priority. The generated switchingsignal is sent to the switching circuit 55.

The switching circuit 55 supplies the current to the base of thepnp-type transistor Q1 or the base of the pnp-type transistor Q2 on thebasis of the switching signal from the low voltage priority circuit 54.Thus, the circuit between the emitter and the collector of thetransistor in which the voltage is equal to or larger than the specifiedminimum input voltage value and the voltage is lower is turned on, thatis, made conductive, and the secondary battery E1 is charged via theresistor R1.

In the embodiment, by the low voltage priority circuit 54, the priorityof the external power source on the side where the power voltage that isinputted is equal to or larger than the specified minimum input voltagevalue and the voltage is lower is set to be higher, the heat generationor the like of the pnp-type transistors Q1 and Q2 is suppressed, and thesafety of the charging circuit is improved. However, the safety of thecharging circuit can be improved by setting the priority of the externalpower source of the lower electric power to be higher.

In such a case, an electric power detecting circuit 60 connected to theQ1 voltage detecting circuit 51, the Q2 voltage detecting circuit 52,and a current detecting circuit 56 shown by broken lines in FIG. 9 isused. The electric power detecting circuit 60 is a circuit for detectingeach electric power on the basis of the detection results of the Q1voltage detecting circuit 51 and the Q2 voltage detecting circuit 52 anda current from the current detecting circuit 56. The electric powerdetecting circuit 60 is also a circuit for preferentially selecting theexternal power source on the side where the detected electric power issmaller and generating a switching signal on the basis of the priority.If such an electric power detecting circuit is used in place of the lowvoltage priority circuit 54, the external power source on the side wherethe detected electric power is smaller can be used selectively.

As described above, in the charging circuit according to the fifthembodiment, if the external power sources are inputted from both theterminal 11 for the external power adaptor and the terminal 12 for theholder and charged, the transistor on the side where the power voltageis equal to or larger than the specified minimum input voltage value andthe voltage is lower between the pnp-type transistors Q1 and Q2 isturned on, the circuit between the emitter and the collector of such atransistor is made conductive, and the current of the power voltage isinputted to the resistor R1 and the collector of the other transistor.At this time, since no base current flows in the other transistor, theother transistor is turned off. Since the voltage that is inputted isalso the backward voltage, it is possible to prevent the current fromflowing from the other transistor. Since the transistor is used as asemiconductor device for preventing the current from the input terminalfor charging from being outputted from the other input terminal forcharging, the voltage drop is smaller than that in the case of using adiode. Therefore, the loss of voltage in the charging circuit can bereduced and the charging efficiency is improved.

Even if the external power sources are inputted from both the terminal11 for the external power adaptor and the terminal 12 for the holderupon charging, since it is possible to control the apparatus in a mannersuch that only the safer external power source is selectively used, theheat generation due to the overcurrent is prevented and the safety ofthe charging apparatus can be held.

A charging apparatus according to the sixth embodiment of the inventionwill now be described. In the charging apparatus according to the sixthembodiment, when the power sources are inputted from the two inputterminals for charging, the external power source on the side where thevoltage of the external power source that is inputted is closer to aninput reference voltage is selectively used. FIG. 10 is a diagramshowing an example of a charging circuit according to the sixthembodiment of the invention. Since the charge power stabilizing circuit,the secondary battery, and the like have already been described in theforegoing second and third embodiments, their explanation is omittedhere. In the charging circuit according to the sixth embodiment, acontrol circuit for the pnp-type transistors Q1 and Q2 is constructed asfollows.

An input voltage detecting circuit 61 is connected between the terminal11 a as a plus electrode and the terminal 11 b as a minus electrode ofthe terminal 11 for the external power adaptor and is a circuit whichcan detect the voltage of the external power source that is inputtedbetween the terminal 11 for the external power adaptor. An input voltagedetecting circuit 62 is connected to the terminal 12 a as a pluselectrode and the terminal 12 b as a minus electrode of the terminal 12for the holder and is a circuit which can detect the voltage of theexternal power source that is inputted to the terminal 12 for theholder.

The input voltage detecting circuit 61 is connected to a differencedetecting circuit 63 and a charge stop circuit 66. The input voltagedetecting circuit 62 is connected to a difference detecting circuit 64and the charge stop circuit 66. The charge stop circuit 66 is connectedto a control circuit 69 and is a circuit for generating a control signalto stop the charge on the basis of detection results of the inputvoltage detecting circuits 61 and 62.

The difference detecting circuits 63 and 64 are connected to a referencevoltage circuit 65. The reference voltage circuit 65 is a circuit inwhich a reference voltage (hereinafter, referred to as a reference inputvoltage value) as an ideal voltage of the external input power sourcethat has been preset has been stored. The difference detecting circuit63 is a circuit for detecting a difference between the reference inputvoltage value of the reference voltage circuit 65 and an input voltagedetected by the input voltage detecting circuit 61. The differencedetecting circuit 64 is a circuit for detecting a difference between thereference input voltage value of the reference voltage circuit 65 and aninput voltage detected by the input voltage detecting circuit 62.

The difference detecting circuits 63 and 64 are connected to a smalldifference detecting circuit 67. The small difference detecting circuit67 is a circuit for comparing the difference calculated in thedifference detecting circuit 63 and the difference calculated in thedifference detecting circuit 64, setting the priority of the externalpower source on the side where the difference is smaller to be high, andgenerating a switching signal corresponding to such a priority. Thesmall difference detecting circuit 67 is connected to a switchingcircuit 68.

The switching circuit 68 is connected to the base of the pnp-typetransistor Q1 and the base of the pnp-type transistor Q2 and is acircuit for supplying a current to the base of the pnp-type transistorQ1 or the base of the pnp-type transistor Q2 and switching the on/offoperations of the pnp-type transistor Q1 or Q2 on the basis of theswitching signal from the small difference detecting circuit 67.

The control circuit 69 is connected to a charge stop signal generatingcircuit 70 and the switching circuit 68. The charge stop signalgenerating circuit 70 is a circuit for generating a charge stop signalon the basis of a control signal from the control circuit 69. The chargestop signal is a signal showing that the apparatus is in a charge stopstate. The charge stop signal generating circuit 70 is connected to anoperation signal generating circuit 71. When the charge stop signal issent from the charge stop signal generating circuit 70, the operationsignal generating circuit 71 generates an operation signal. Theoperation signal generating circuit 71 is connected to the smalldifference detecting circuit 67.

In the charging circuit according to the sixth embodiment, subsequently,the operation in the case where the external power sources are inputtedfrom the input terminals of both the terminal 11 for the external poweradaptor and the terminal 12 for the holder upon charging will bedescribed.

In the charging circuit, in the case of charging by using the terminal11 for the external power adaptor and the terminal 12 for the holder,the currents of the external power voltages are inputted from theterminals 11 a and 12 a. The current of the external power voltageinputted from the terminal 11 a flows in the emitter of the pnp-typetransistor Q1 and the input voltage detecting circuit 61. Therefore, theinput voltage detecting circuit 61 detects the external power voltagethat is inputted to the terminal 11 for the external power adaptor.

The current of the external power voltage inputted from the terminal 12a flows in the emitter of the pnp-type transistor Q2 and the inputvoltage detecting circuit 62. Therefore, the input voltage detectingcircuit 62 detects the external power voltage that is inputted from theterminal 12 for the holder. A detection result of the input voltagedetecting circuit 61 is sent to the difference detecting circuit 63 andthe charge stop circuit 66. A detection result of the input voltagedetecting circuit 62 is sent to the difference detecting circuit 64 andthe charge stop circuit 66.

In each of the difference detecting circuits 63 and 64, the differencebetween the detected input voltage and the reference voltage from thereference voltage circuit 65 is detected. Each detection result is sentto the small difference detecting circuit 67.

The small difference detecting circuit 67 is made operative by theoperation signal from the operation signal generating circuit 71. Thatis, when the detection signals are sent to the charge stop circuit 66from both of the input voltage detecting circuits 61 and 62, the chargestop circuit 66 transmits a signal for stopping the charge to thecontrol circuit 69. When the control circuit 69 receives the charge stopsignal, it sends a switching signal for stopping the charge to theswitching circuit 68, thereby stopping the charge to the secondarybattery E1.

The control circuit 69 sends a signal indicative of the charge stopstate to the charge stop signal generating circuit 70 when the charge isstopped. When the charge stop signal generating circuit 70 receives sucha signal, it generates the charge stop signal and sends it to theoperation signal generating circuit 71. When the operation signalgenerating circuit 71 receives the charge stop signal, it generates anoperation signal and sends it to the small difference detecting circuit67. Thus, the small difference detecting circuit 67 is made operative.

In the small difference detecting circuit 67, the external power sourceon the side where the difference is smaller, that is, the power sourceon the side where the voltage is close to the reference voltage, ispreferentially selected, and the switching signal is generated on thebasis of the priority. The switching signal is sent to the switchingcircuit 68.

The switching circuit 68 supplies a current to the base of the pnp-typetransistor Q1 or the base of the pnp-type transistor Q2 on the basis ofthe switching signal from the small difference detecting circuit 67.Thus, the circuit between the emitter and the collector of thetransistor to which the external power source that is closer to thereference voltage is inputted is turned on, that is, is made conductive,and the secondary battery is charged.

As described above, in the charging circuit according to the sixthembodiment, in the case where the external power sources are inputtedfrom both the terminal 11 for the external power adaptor and theterminal 12 for the holder and the charge is executed, the transistor onthe side where the external voltage which is closer to the referenceinput voltage between the pnp-type transistors Q1 and Q2 is inputted isturned on. The circuit between the emitter and the collector of such atransistor is made conductive, and the current of the power voltage isinputted to the collector of the other transistor and the secondarybattery (not shown). At this time, since no base current flows in theother transistor, the other transistor is turned off. Since the voltagethat is inputted is also the backward voltage, it is possible to preventthe current from flowing from the other transistor.

Since the transistor is used as a semiconductor device for preventingthe current from the input terminal for charging from being outputtedfrom the other input terminal for charging, the voltage drop is smallerthan that in the case of using a diode. Therefore, the loss of voltagein the charging circuit can be reduced and the charging efficiency isimproved.

Even if the external power sources are inputted from both the terminal11 for the external power adaptor and the terminal 12 for the holderupon charging, since the apparatus can be controlled so as toselectively use only the external power source which is closer to thereference input voltage, the heat generation or the like due to theovercurrent can be prevented and the safety of the charging apparatuscan be held.

Subsequently, a charging apparatus according to the seventh embodimentof the invention will be described. According to the charging apparatusof the seventh embodiment, when the external power sources are inputtedfrom the two input terminals for charging, if the total current of thetwo inputs is equal to or less than a reference value, the charge isperformed from both the external power sources, and if the total currentof the two inputs exceeds the reference value, the charge is performedfrom only one of the external power sources.

FIG. 11 is a diagram showing an example of a charging circuit accordingto the seventh embodiment of the invention. In the charging circuitaccording to the seventh embodiment, control circuits for the pnp-typetransistors Q1 and Q2 are constructed as follows.

A current detecting circuit 77 and an overcurrent detecting circuit 76are connected to both ends of the resistor R1. The current detectingcircuit 77 is a circuit for detecting the charge current to thesecondary battery E1. The overcurrent detecting circuit 76 is alsoconnected to both ends of the resistor R1. The overcurrent detectingcircuit 76 is a circuit for detecting an overcurrent to the secondarybattery.

The current detecting circuit 77 is connected to an operation switchingcircuit 74. The operation switching circuit 74 is a circuit fordiscriminating whether the operation is switched to only one operationor not on the basis of a detection result of the current detectingcircuit 77. The operation switching circuit 74 is connected to aone-operation stop circuit 75. The one-operation stop circuit 75 is acircuit for generating a control signal on the basis of a discriminationresult that is supplied from the operation switching circuit 74 andshows whether one of the operations is stopped or not. The one-operationstop circuit 75 is connected to an operation detecting circuit 78 and isa circuit for transmitting an operation signal to the operationdetecting circuit 78 during the operation of the one-operation stopcircuit 75. The operation detecting circuit 78 is connected to theovercurrent detecting circuit 76 and is a circuit for controlling theoperation of the overcurrent detecting circuit 76 on the basis of adetection result of the operation detection signal.

The overcurrent detecting circuit 76 is connected to an operation stopcircuit 79 and is a circuit for transmitting an operation signal to theoperation stop circuit 79 during the operation of the overcurrentdetecting circuit 76. The operation stop circuit 79 is connected tocontrol circuits 72 and 73, detects the operation signal from theovercurrent detecting circuit 76, and sends the operation stop controlsignal to the control circuits 72 and 73.

The one-operation stop circuit 75 is connected to the control circuits72 and 73 and is a circuit for transmitting a control signal for turningoff one of the pnp-type transistors Q1 and Q2 to the control circuit 72or 73. The control circuit 72 is connected to the base of the pnp-typetransistor Q1 and is a circuit for controlling the base current to thepnp-type transistor Q1 and switching the on/off operations of thepnp-type transistor Q1 on the basis of the control signal. The controlcircuit 73 is connected to the base of the pnp-type transistor Q2 and isa circuit for controlling the base current to the pnp-type transistor Q2and switching the on/off operations of the pnp-type transistor Q2 on thebasis of the control signal.

A constant voltage detecting circuit 80 is connected to both ends of thesecondary battery E1. The constant voltage detecting circuit 80 isconnected to the control circuits 72 and 73 and is a circuit fordetecting a constant voltage from the voltage to be charged andtransmitting a detection result to the control circuits 72 and 73. Sincethe charge power stabilizing circuit (not shown) has already beendescribed in the foregoing second and third embodiments, its explanationis omitted here. In the charging circuit according to the seventhembodiment, subsequently, the operation in the case where the externalpower sources are inputted from the input terminals of both the terminal11 for the external power adaptor and the terminal 12 for the holderupon charging will be described.

In the foregoing first to sixth embodiments, before the connection ofthe external power sources, both of the pnp-type transistors Q1 and Q2are always set to the OFF state, and one of them is turned on inaccordance with a predetermined condition. In the seventh embodiment,before the connection of the external power sources, both of thepnp-type transistors Q1 and Q2 are always set to the ON state and one ofthem is turned off when the overcurrent is detected.

That is, in the charging circuit, in the case of charging by using theterminal 11 for the external power adaptor and the terminal 12 for theholder, the currents of the external power voltages are inputted fromthe terminals 11 a and 12 a. The current of the external power voltageinputted from the terminal 11 a flows in the secondary battery E1 viathe pnp-type transistor Q1. The current of the external power voltageinputted from the terminal 12 a flows in the secondary battery E1 viathe pnp-type transistor Q2.

During the charge, the charge current is detected by the currentdetecting circuit 77. The detected current is sent to the operationswitching circuit 74 and whether the current value is equal to or largerthan a reference current or not is discriminated. If it is equal to orlarger than the reference current, the operation switching circuit 74sends an operation switching signal to the one-operation stop circuit75. On the basis of the operation switching signal, the one-operationstop circuit 75 generates a control signal for turning on only one ofthe pnp-type transistors Q1 and Q2.

The control signal generated by the one-operation stop circuit 75 issent to the control circuits 72 and 73. By the control signal, thecontrol circuits 72 and 73 supply the base current to only one of thepnp-type transistors Q1 and Q2 so as to select one of the external powersources to be charged. At this time, which one of them is preferentiallyused also can be determined by applying the foregoing first to sixthembodiments.

As mentioned above, the one-operation stop circuit 75 detects theoperation signal from the operation switching circuit 74, and during theswitching operation of the power sources, the one-operation stop circuit75 sends the operation signal to the operation detecting circuit 78.When the operation signal is detected, the operation detecting circuit78 sends a temporary stop signal to the overcurrent detecting circuit76. By the temporary stop signal from the operation detecting circuit78, the overcurrent detecting circuit 76 enters a temporary stop modewhen the operation is switched to the input of only one power source.After the stop of the switching operation of the power sources, that is,when the one-operation stop circuit 75 does not detect the operationsignal from the operation switching circuit 74, the one-operation stopcircuit 75 stops the transmission of the operation signal to theoperation detecting circuit 78 and the overcurrent detecting circuit 76is made operative.

During the operation of the overcurrent detecting circuit 76, theovercurrent detecting circuit 76 sends the operation signal to theoperation stop circuit 79 and sends the operation stop signal to thecontrol circuits 72 and 73. By the operation stop signal, the powerswitching operation is stopped during the detection of the overcurrent.Thus, the power sources can be switched while protecting the pnp-typetransistors Q1 and Q2 or the like. The constant voltage across thesecondary battery E1 that is detected by the constant voltage detectingcircuit 80 is sent to the control circuits 72 and 73. The secondarybattery E1 is charged by the external power source of the voltagesuitable for charging.

As described above, in the charging circuit according to the seventhembodiment, since the external power sources are inputted from both theterminal 11 for the external power adaptor and the terminal 12 for theholder and charging, it is possible to prevent the current from flowinginto the outside from the charging input terminals.

If the total current of the two external power sources is equal to orless than the reference current, since the charging is performed byusing both of the external power sources, the battery can be efficientlycharged.

Since the transistor is used as a semiconductor device for preventingthe current from the input terminal for charging from being outputtedfrom the other input terminal for charging, the voltage drop is smallerthan that in the case of using a diode. Therefore, the loss of voltagein the charging circuit can be reduced and the charging efficiency isimproved.

The invention is not limited to the foregoing embodiments or the like ofthe invention, but many variations and modifications are possible withinthe scope of the invention without departing from the spirit of theinvention. For example, the pnp-type transistors Q1 and Q2 are notlimited to the pnp-type transistors and can be replaced with othersemiconductor devices, such as FETs (Field Effect Transistors) or thelike, each having an input electrode, an output electrode, and a controlelectrode to control the output electrode.

For instance, although the two terminals, such as terminal 11 for theexternal power adaptor and the terminal 12 for the holder, have beenused as charging input terminals, the invention is not limited to them,but the battery can be also charged from three or more input terminalsfor charging.

For example, although the example of using the cellular phone as aportable electronic apparatus having the charging apparatus according tothe invention has been described in the above embodiments, the inventionis not limited to it, but the invention can be also applied to otherapparatuses, such as a MD player, a PDA (Personal Digital Assistants), avideo camera, and the like.

As described above, according to the invention, in the chargingapparatus having two or more input terminals that are used for charging,by switching the on/off of the inputs of the external power sources byusing a semiconductor device, such as a transistor having an inputelectrode, an output electrode, and a control electrode for controllingthe output electrode, the secondary battery can be efficiently chargedwhile keeping safety.

If the external power sources are inputted from a plurality of inputterminals for charging, by allocating the priorities to them inconsideration of the safety of the charging operation and its chargingefficiency, selectively using the external power source having thehigher priority, and charging the battery, the secondary battery can beefficiently charged while maintaining safety.

In the case where the external power sources are inputted from aplurality of input terminals for charging, if the total current value ofthe inputted external power sources is smaller than the input referencepower source, the external power sources are inputted from a pluralityof input terminals for charging. If the total current value is equal toor larger than the input reference power source, by selectively usingthe external power sources, the secondary battery can be efficientlycharged while maintaining safety.

The present invention is not limited to the foregoing embodiments, butmany modifications and variations are possible within the spirit andscope of the appended claims of the invention.

1-9. (canceled)
 10. A charging apparatus comprising: first and secondinput terminals to which power voltage sources are connected; first andsecond semiconductor devices for power control in which said first andsecond input terminals are connected to input electrodes, respectively;a secondary battery to which output electrodes of said first and secondsemiconductor devices for power control are connected in common andwhich is connected between said common connection electric potentialpoint and a reference electric potential point; a control circuit forcontrolling a terminal voltage and a charge current of said secondarybattery to desired values; and switching signal generating means fordetecting voltages which are generated at the input electrodes of saidfirst and second semiconductor devices for power control and generatinga switching signal for turning on a circuit between the input and outputelectrodes of said semiconductor device for power control at which thevoltage has been detected, wherein if the voltages are detected from theinput electrodes of both of said first and second semiconductor devicesfor power control, the input power sources are controlled by turning onthe circuit between the input and output electrodes of one of said firstand second semiconductor devices such that in accordance with a priorityprotocol the semiconductor device located on the side in which thevoltage is equal to or larger than a predetermined minimum voltage valueis selected, and wherein said first and second input terminals are aterminal for connecting an AC adaptor and a terminal for a holder.